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Pro: I can reduce the storage size (due to company size limit policy)
Con: I won't be able to organize my emails to different folders.

Anyone has comments on my GTD method?

Can't comment on the Pro side of the equation, I keep all e-mails and have for years. I have gone back as far as 15 years or more for e-mails as reference. But on the cons. I found that fewer folders is a lot better. So I save all my e-mail from lists that are single topic related in folders for that list but everything else just goes into one big reference folder. It reduces the places to look when I need something.

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If you are currently moving all emails to your task manager creating your own to do lists, when you categorize your email you have already processed it so in seem useless to keep it stored in your email folders.

After the issue is done you can archive it in a folder. Keep in ming that as less folders you have better! So if you can work it out with one general archive that's the way to go!

It seems to me that you have experienced a gigantic step forward: you have managed to adapt GTD method to your own outlook usage, therefore creating a couple of "must have" folders that really are of no use to you! Keep working on your system and be alert to things that serve you (and reinforce them) and things that don't (and drop them).